Hello all,
I have a Tek 475A whose CH1 bandwidth falls off as the input frequency increases. At 200MHz, the vertical amplitude is about half of what it should be. CH2 is working fine. The fault seems to exist no matter what the vertical sensitivity is so I don't think that it's the extenuator, and the 100 and 20MHz bandwidth limiter also appear to be working. Does this fault suggest anything in particular to the experts out there?
Thanks!
Ahem. Attenuator
Spell checkers...
JW wrote in news: snipped-for-privacy@4ax.com:
If the problem is just on Ch1,then you have a problem in Channel 1. Ch 1 and 2 don't combine until the delay line driver/channel switch,IIRC.
the tiny HF trimmer caps in the 400 series had a habit of developing a black oxide underneath them that effectively insulates the rotor from the solder pin,making the cap -open-.(and no effect when adjusted) They also would freeze so they could not be turned without breaking the screwhead loose from the rotor disc .
essentially,you have to replace the bad trimcaps. Then recal per the cal procedure.
-- Jim Yanik jyanik at kua.net
:
Have you swapped probes??
"hr(bob) snipped-for-privacy@att.net" wrote in news: snipped-for-privacy@p43g2000hsc.googlegroups.com:
you shouldn't be testing/calibrating BW using probes. you use a levelled signal generator,50ohm coax,a 50 Ohm feedthru termination,and appropriate 50ohm attenuators.
-- Jim Yanik jyanik at kua.net
Thanks, Jim. Given the age of this scope and lack of a schematic/service manual, I think I'll just scrap it.
[...]
Yup.
JW wrote in news: snipped-for-privacy@4ax.com:
doesn't the BAMA site have any 475 manuals?
475's were good scopes;I doubt you'll find any new scopes as good.-- Jim Yanik jyanik at kua.net
Where are you located? I'd love to take a shot at it as my only modern portable as an ailing B&K 20 MHz scope.
Regards,
Michael
Yeah, but only operators...
I'm sure that I can use parts from this one to fix the next one to come across my bench. I work as a tech for a test equipment salvage company, and I'd have to be able to justify my time and cost of calibration for this to be worthwhile. Not having the service manual (or having to pay for one) on a scope of this vintage just isn't worth it.
Well, as I said in my other post, this will be used as a parts unit. (It's not my scope.)
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